comp not loading after powered on

I am so frustrated with comp of hubby. Yesterday we had no problems at all. Tonite we go to get on and it will power on but not boot. then after about 3 or 4 tries we finally get it to boot up just to have it shut down once the desktop loaded. We have checked all the wires and cables, checked out with a different hard drive--still same condition. We have tried changing jumpers and settings, with no luck of change we put settings back to original. The only thing recent that has been done, was about a month ago we put a new cpu fan on. But this is first prob we have had. Does anyone have a clue as to what could be problem or what we should check next. i hope it isnt the processor or mb any help would be greatly appreciated the fan light is also on solid, bios light is on solid on my card tester. do not hear any beeps when powering on. also hear a chirping noise when move one cable---not sure where it goes